Static elimination in manometers



1949- c. FL WALLACE 2,462,820

STATIC ELIMINATION IN MANOMETERS Filed March 12, 1945 V v INVENTOR.679491.555 #1440105 4 flW/w. 4%

1i TZjORA/Ey Patented Feb. 22, 1949 UNITED STATES PATENT OFFICE STATICELIMINATION IN MANOME'IERS Charles F. Wallace, Westfield, N. J assignorto Wallace & Tier-nan Products, Inc., Bclleville, N. J., a corporationof New Jersey Application March 12, 1945, Serial No. 582,340

2 Claims.

My present invention relates to static elimination in manometers andmore particularly to manometers such, for example, as a mercurybarometer, wherein means are provided for pre- 2 opposite sign, i. c.either negative or positive (respectively). It has been suggested that atheory tending to explain this phenomenon is that the mercury does notwet the tube and hence does Venting the effect p t e h of the e c y 5not have such contact therewith as can bleed an column of staticelectricity which causes some inelectrical charge from the inside wallsof the accuracies in the readings. tube. However, the present inventionis not In working with manometers, particularly merpredicated upon anyparticular theory; and this cury barometers, it has been found that thepresis only suggested by way of possible explanation. ence of staticelectricity inside the transparent A further and more specific object ofthe prestube conta a column of liq id, the height of out invention is toprovide an inside coatin on which is indicative of a pressure or othercondition a manometer tube of the above described characto be measured,causes relatively small, but appreter, which will be in close contactwith the lube ciable, errors in the height of the liquid column. andwill be per se electrically conducting, while For example, in a mercurybarometer, this error being sufficiently transparent or translucent, soas may be in the order of magnitude of .005 inch to permit avisualreading of a height of the liquid of mercury. Where the utmost accuracyis of imcolumn in the tube and so that any static elecportance, it isnecessary that means be provided tricity which may accumulate inside atube by for eliminating this error. The provision of such reason of theliquid ther in being moved up and means is a primary object of thepresent invendown or for any other reason, may be bled off to tion. asuitable ground so that it will not interfere with The presence ofstatic electricity has been noted the liquid column attaining a levelaccurately inin the following way. If a small piece of very thindicative of the magnitude of a condition to be inaluminum foil iscemented on the upper edge only dicated thereby. to the side of a tubeand is bent so that its bottom Other and more detailed objects of thepresent edge is approximately /8 from the tube such as invention willbecome apparent from the follow a glass tube containing a mercury columnand the ing specification and appended claims, whentaken mercury run upor down several times past the in connection with the accompanyingdrawin s, in place at which the aluminum foil is secured, it will which:be found that when the mercury rises upwardly Figure 1 is afore-shortened view, partly in past the aluminum foil, the uncementedpart of elevation and partly in central vertical section, the latterwill remain outwardly away from the showing a portion of a mercurybarometer wheretube; and when the mercury is moved down past in the tubeis coated interiorly in accordance this foil, it will move toward thetube and stay with the present invention; and close to the glass. When,however, a tube used for Fig. 2 is a detail view in horizontal sectionon a liquid column to measure pressure is treated as the line 22 ofFig. 1. hereinafter more particularly set forth and in ac- I have chosento illustrate my invention as apcordance with the present invention,this eifect is plied to a mercury barometer, although I contemnotpresent. Further, upon comparison between plate that it is equallyapplicable to any and all an untreated manometer and one constructed ortypes of manometers and also may be applicable prepared in accordancewith the present invento manometers using liquids other than mercury.tion, it is found that the untreated manometer The drawings illustrate amercury barometer usually shows a higher readin if it has been includinga container l, which may be constructused recently, in the order ofmagnitude of .005 ed in the usual manner to contain a pool of merinch ofmercury, than that of the treated manomcury and which may have anopening to the eter. The fact that the mercury itself is elecatmospherethrough a top portion 2 thereof or trically conducting apparently doesnot serve to may be connected in a manner (not shown) to a bleed suchstatic electricity away from the survessel in which there is a gaseouspressure which face of the tube in which it is enclosed, as the it isdesired to indicate. There is provided a tube phenomenon has beenparticularly noticed as 3 in the usual manner, which preferably extendsaforesaid in connection with mercury barometers. dOWn n o a p o ofmercury de t e n ainer It is assumed, but not herein relied upon that inI, but does not extend completely to the bottom the case of mercurymanometers at least, the thereof, this tube preferably being oftransparent mercury has a charge of one sign (either positive 5 ortranslucent material such as glass. The indior negative) while the glasshas a charge of the eating liquid, in this case mercury, is shown at 4up to a height or level indicated at 5 in the tube. Thus, if the levelof the mercury in the container l is maintained at a given point in anysuitable manner known to the art, the height of the column of mercury 4,that is the level or top surface 5, may be read in connection with anappropriate gauge or scale in any desired and/ or known manner. Theconstruction thus far described may be considered as the standardequipment of the prior art.

As above set forth, I have found that the presence of static electricitywhich tends'to collect on the inside surface of the tube 3 causes theerror in the height of the mercury column, which tends to cause it toread high and by an amount which has been found to be in the order ofmagnitude of .005 inch.

My present invention provides means for bleeding off this staticelectricity, so that it will not interfere with or affect the height ofthe column. For this purpose I preferably provide on the inside surfaceof the tube 3 a coating of some electrically conductive material, whichpreferably also is sufficiently transparent or translucent so that theheight of the liquid, that is the level 5, may be visually read orotherwise ascertained. While I contemplate that various types ofcoatings might be adequate for this purpose, including sprayed metal,the type I have found most advantageous for practical use is a thin filmdeposited from an aqueous colloidal solution of graphite, such as thatknown commercially as Aquadag. This coating is shown diagrammatically inthe accompanying drawings at 6. It will be understood that while thelayer ii as shown in the drawings is of substantial thickness, this isfor illustrative purposes only and is not to be taken as .an accurateillustration indicative of the actual dimensions of the thickness of thecoating which is in practice very thin, so that it will not seriouslyinterfere with the transparency r transluency of the coated tube andthus interfere with a visual reading of the height of the top surfacelevel of the liquid column. Preferably the entire interior surface ofthe tube is coated, although I contemplate that if only that portionextending for a substantial distance above and below the probable heightof the liquid column 5, many, if not all, the desired results of thisinvention would still be attained. In view of the fact that most liquidsused in manometers are per se to some extent electrically conducting, ithas been found that there will be a sufiicient contact if the tube iscoated for a substantial length below the surface of the liquid 5 toeffect a bleeding off and consequent grounding of the static electricityfrom the layer or coating 6 to the fluid itself.

While I have shown and specifically described herein but one embodimentof the present invention and have pointed out in connection with thisdescription the essential characteristics thereof,

it will be understood that various modifications may be made thereinwithin the above teachings and as will be apparent to those skilled inthe art therefrom. I do not wish to be limited, therefore, except by thescope of the appended claims, which are to be construed validly asbroadly as the state of the prior art permits.

What I claim is:

1. A manometer, comprising a non-metallic and non-electric conductingtube containing a liquid, the level of the surface of which in said tubeis indicative of the magnitude of a condition, and an electricallyconducting coating inside said tube and. in contact with said tube andwith the liquid therein for bleeding off static electricity on theinside of said tube, so as to prevent any effect of such staticelectricity upon the level of the surface of the liquid in'said tube.

2. A manometer in accordance with claim 1, wherein said tube is atransparent glass tube, said coating is a substantially transparentlayer of graphite, and said liquid is mercury.

CHARLES F. WALLACE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 127,752 Emery et a1 June 11, 1872379,305 Brown Mar; 13, 1 888 546,802 Ayrton et al. Sept. 24, 1895815,814 Green Mar. 20, 1906 2,346,483 Goss Apr. 11, 1944

